The present invention relates to a system and process for effecting the rapid charging of a battery of sealed storage cells. The present invention also relates to an assembly for permitting the rapid charging of a battery of sealed storage cells comprising a charger and means incorporated in the battery cooperating with the charger to control the latter.
It will readily be understood that a battery of storage cells will satisfy a wider range of application requirements, whether in industrial or in everyday life, if it is capable of being rapidly recharged. The physical problems relating to the rapid charging of sealed storage cells are concerned essentially with the inner pressure of the sealed storage cell and the temperature thereof; an excessively high internal pressure or an excessively high temperature may result in damage to the storage cell. In order not to exceed the safe limiting value permitted for the pressure, it is necessary to know that the charging state of the battery, determined by the value of its charging parameters such as the voltage across the terminals of the storage cell or cells and their temperature. These two charging parameters, i.e. temperature of the storage cell or cells and charging voltage, are not independent; during the final phase of rapid charging, the internal temperature of the storage cell increases, as does also the voltage across the terminals of the battery, and the problem which arises is how to interrupt the rapid charging rate at an opportune instant. This instant should be, on the one hand, sufficiently late to ensure that the battery or cell is either completely charged, or else charged to a sufficient percentage of its total charge and, on the other hand, of course, should be sufficiently timed to ensure that the battery will not be damaged.
Some known processes for the rapid charging of storage cells consist in charging the storage cell at a rapid rate and partially discharging it extremely rapidly and at extremely short intervals during charging, in such manner as to monitor the potential difference across the terminals of the storage cells. In the case of sealed nickel-cadmium storage cells, this known process makes it possible to interrupt high rate charging before the potential of the negative electrode reaches the threshold corresponding to hydrogen evolution. However, the devices for the carrying into effect of these processes are complex and costly. Other processes also have been proposed for the rapid charging of sealed storage cells; for example, one of the said processes, disclosed in French Pat. No. 1,565,095, filed on the 26th Apr. of 1968 in the name of GENERAL ELECTRIC COMPANY, and corresponding to U.S. Pat. No. 3,531,706 consists in charging the battery during every other half-wave, measuring the voltage across the terminals of the storage cells during the other half-wave during which the battery is not being charged, detecting the temperature of the storage cells with the aid of a blade thermistor and, with the aid of a blade switch opening the charging circuit before there is any risk of damage to the cell. The disclosed device of this specification, although it permits rapid charging of sealed storage cells, nevertheless has the disadvantage that it does not afford adequate reproducibility to permit the employment of the same charger for charging a plurality of batteries.
On the other hand, when a rapid charger is connected to the a. c. mains, it is current practice to feed the charger through intermediary of a magnetic leakage transformer or through the intermediary of a conventional transformer and a stabilization inductance. For a charger designed to charge a battery of storage cells of relatively high power, equipment of this kind is heavy and a charger fitted with a transformer represents a weight which renders the utilization thereof inconvenient in practice.
The present invention makes it possible to obviate these disadvantages and provides a rapid-charging device for sealed storage cells which is of great simplicity and has a high degree of reliability. The novel device or system permits the charging of the storage cell or battery during a reduced period of time for obtaining almost complete charging. Furthermore, the device or system is equipped with a slow charging circuit permitting the completion of charge after rapid charging has been halted. The device or system according to the invention comprises means for reliably interrupting rapid charging before the occurrence of any risk of damage to the cell or cells. Finally, according to an embodiment of the invention, the charger is readily transportable due to the elimination of the feed transformer.